Cement sets by hydration reactions forming C-S-H gel and Ca(OH)₂, even underwater. It's a chemical process, not drying. Gypsum controls the setting rate.
Explanation:
H₂O₂ releases oxygen that kills bacteria (antiseptic) and bleaches colored materials. Ethanol is disinfectant but not strong bleach. Methanol is toxic.
Explanation:
The unwanted earthy or sandy impurities present in an ore are called gangue (or matrix). Flux is added during smelting to react with these impurities, and the resulting fused mass is called slag, which is lighter and floats on top of the molten metal for easy removal.
Explanation:
Tropospheric ozone is not emitted directly; it forms by photochemical reactions of NOx and VOCs in sunlight. So it's a secondary pollutant. CO, SO₂, and lead are primary pollutants emitted directly from sources. Secondary pollutants include ozone, PAN (peroxyacetyl nitrate), and sulfuric acid mist. Ozone at ground level is harmful.
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